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lew247

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Joined: 23/12/2015
Location: United Kingdom
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Posted: 05:32pm 13 Sep 2019

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I;ve tried 3 different BME280 modules now in case I have a faulty one and all of them give the same results
The readings are higher than the actual temperature, by around 2-3�C
I have tested it with my Weatherflow Sensor beside the BME280, a glass thermometer sat in the same place and a BME280 on a Pi Zero using Python and they all give around the same temperatures around 2-3�C lower than the MM

The MM is on Pi Zero W using Matherps latest Picromite and the BME280 code thats on the forum

Anyone else found this or have any idea why?

I've mounted the BME280 sensor physically away from the Pi so it can't be heat from the PI affecting it.

TassyJim

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Joined: 07/08/2011
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Posted: 10:25pm 13 Sep 2019

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I have a BMP280 co-located with a SHT31.
The BMP280 is consistently 1 degree higher than the SHT31

I put it down to the BMP280 mainly interested in it's internal temperature which it uses for pressure and humidity readings.

The SHT31 uses Arduino code and the BME280 is on a MX170

Jim

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PeterB
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Joined: 05/02/2015
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Posted: 01:38am 14 Sep 2019

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Back in Feb. I took readings from 2, BME with 170 and decided the error was less than 0.5C.

Peter

goc30

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Joined: 12/04/2017
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Posted: 04:19pm 14 Sep 2019

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I also found this problem (+2/3 DegC), including with a rpi3, and even an arduino
I think it come from chinese product quality with low cost components

PeterB
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Posted: 12:32am 15 Sep 2019

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Good morning Lew.

I just read your post correctly this time.
The actual problem is with the MM not the BME280, correct?
It is reading 2-3 degrees higher than true.
If that is the case then:

1. check code
2. check soldered joins & mechanical connections
3. prayer

Peter

robert.rozee
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Joined: 31/12/2012
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Posted: 12:54am 15 Sep 2019

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might i suggest the following test:

place a BMP280, a DS18B20, and a SHT31 - all wired up to a remove micromite - into a small polystyrene box, along with something to act as a thermal mass. sand would to. leave for half a day and check the temperature reading produced by each.

you'll find that different constructions of sensor may behave differently in free air. things like exposed metal surfaces (BMP280), a plastic shell (SHT31), and a thermall small mass (DS18B20) will effect how small movements of air impact the reading.

cheers,
rob :-)

TassyJim

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Joined: 07/08/2011
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Posts: 5898

Posted: 02:40am 15 Sep 2019

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I had a spare BME280 so I added it to my test micromite. (The one accessible from MMEDit)

Quote 12:39:14 T(BMP180): 22.1 P(sl): 1011.5,T(DHT22): 21.4 H: 48.9,T(DS18B20): 23.5 BME280: T: 23.1 P: 1011.0 H: 43.7
12:39:24 T(BMP180): 22.1 P(sl): 1011.4,T(DHT22): 21.4 H: 49.0,T(DS18B20): 23.2 BME280: T: 23.1 P: 1011.0 H: 43.8
12:39:34 T(BMP180): 22.1 P(sl): 1011.4,T(DHT22): 21.4 H: 49.1,T(DS18B20): 23.2 BME280: T: 23.1 P: 1011.0 H: 43.9

The test micromite is not in a case and the sensors are in free air reasonably close to each other.

Jim

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PeterB
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Posted: 06:31am 15 Sep 2019

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I think it was 23.1 +/- 0.5 at your place.

Peter

lew247

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Joined: 23/12/2015
Location: United Kingdom
Posts: 1676

Posted: 01:32pm 16 Sep 2019

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Sorry the title of this post is wrong - it should be PI-Cromite not Micromite

I have just got a genuine expensive BME280 just in case any of the others I tried are faulty and I still get the same results

It varies from aroun 3�C high to 4�C higher than the actual temperature

I have tried this so it's eliminated any heat produced by anything

I have it set on a table with a fan blowing air slowly past it, the BME280 is not in any case or packaging it's open to the air on the table

Then I put the glass thermometer in the same spot and took readings

Then I put my Weatherflow Temperature sensor in the same spot and took readings
and finally I used a Fluke multimeter with temperature sensor and took readings

All devices were within 1�C of each other apart from the BME280 mounted on the Pi board

I've used the same BME280 on the same board but using Python instead of MM Basic and it gives a temperature very close to the other devices

I've tried altering the speed of the I2C bus in case that might be causing it but it doesn't help

Anyone got any ideas?

The only thing I can think of is the self calibration in MM is slightly out when using a Pi Zero?

Volhout
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Joined: 05/03/2018
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Posted: 01:58pm 16 Sep 2019

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Dear lew247,

I recall reading a note about the PI running MMbasic. When MMBasic is idle, it still consumes some power.
Maybe that could explain the 3 degrees difference between python and MMBasic.
Local heating by the PI core. You could simply check this by measuring the power from the USB. That heat goes somewhere..

Regards,

Volhout

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lew247

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Posted: 02:13pm 16 Sep 2019

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Volhout said Dear lew247,

I recall reading a note about the PI running MMbasic. When MMBasic is idle, it still consumes some power.
Maybe that could explain the 3 degrees difference between python and MMBasic.
Local heating by the PI core. You could simply check this by measuring the power from the USB. That heat goes somewhere..

Regards,

Volhout

I've eliminated any heat produced by anything

I have it set on a table with a fan blowing air slowly past it, the BME280 is not in any case or packaging it's open to the air on the table

TassyJim

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Joined: 07/08/2011
Location: Australia
Posts: 5898

Posted: 09:58pm 16 Sep 2019

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Can you run the same code on a micromite to see if there is a similar difference in readings.
If there is a difference, you can then print the calibration values etc to see where things deviate between the platforms.

I don't have a PiZero so can't do it here.

I find my BME280 reads higher than the others when there is more air movement.
When there is little air flow, the difference between the various modules is much less.

This is this mornings test:

Quote 07:46:51 T(BMP180): 14.0 P(sl): 1028.5,T(DHT22): 13.7 H: 45.5,T(DS18B20): 14.0 BME280: T: 15.1 P: 1028.4 H: 42.7
07:47:01 T(BMP180): 14.0 P(sl): 1028.6,T(DHT22): 13.7 H: 45.4,T(DS18B20): 14.0 BME280: T: 15.2 P: 1028.3 H: 42.8
07:47:11 T(BMP180): 14.0 P(sl): 1028.7,T(DHT22): 13.7 H: 45.4,T(DS18B20): 14.0 BME280: T: 15.2 P: 1028.3 H: 42.7
07:47:21 T(BMP180): 14.0 P(sl): 1028.5,T(DHT22): 13.7 H: 45.5,T(DS18B20): 14.0 BME280: T: 15.2 P: 1028.3 H: 42.6

A copy of the code you are using will help.

Jim
Edited 2019-09-17 08:01 by TassyJim

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TassyJim

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Posts: 5898

Posted: 04:44am 17 Sep 2019

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OK Lew,
I have had a play.
The following program needs to be run on your PI as well as a micromite using the same BME280 module.
You can then compare the registers and see where there are differences.
The cal%(x), Tx Px and Hx values should be the same for the same module but differ between modules.

The adc%(x) values depend on the temperature etc so will be different for each run.

If you need further investigation, we can take dig into the maths further and see where the figures diverge.

Quote ' BME280 test program to compare Pi-cromite to micromite basic
OPTION BASE 0
OPTION EXPLICIT

' BME280 constants
'
CONST BME280_ADDRESS = &H76
CONST BME280_REGISTER_T1 = &H88
CONST BME280_REGISTER_P1 = &H8E
CONST BME280_REGISTER_H1 = &HA1
CONST BME280_REGISTER_H2 = &HE1
CONST BME280_REGISTER_CHIPID = &HD0
CONST BME280_REGISTER_CONTROLHUMID = &HF2
CONST BME280_REGISTER_CONTROL = &HF4
CONST BME280_REGISTER_PRESSUREDATA = &HF7
CONST BME280_REGISTER_TEMPDATA = &HFA
CONST BME280_REGISTER_HUMIDDATA = &HFD
'
DIM INTEGER s16=&HFFFFFFFFFFFF0000 , s16b=&H8000
DIM INTEGER s12=&HFFFFFFFFFFFFF000 , s12b=&H800
DIM INTEGER s8= &HFFFFFFFFFFFFFF00 , s8b=&H80
'
DIM INTEGER T1,T2,T3 'uint16_t, int16_t, int16_t
DIM INTEGER P1,P2,P3,P4,P5,P6,P7,P8,P9 'uint16_t, 8 x int16_t
DIM INTEGER H1,H2,H3,H4,H5,H6 'uint8_t, int16_t , uint8_t, int16_t, int16_t, int8_t
DIM INTEGER t_fine
DIM FLOAT t_bme, p_bme, h_bme, alt = 235 ' your altitude in metres

I2C OPEN 400, 200 ' Enable I2C. use slow speeds for long leads
PAUSE 20
PRINT "Device = ";MM.DEVICE$
bme280_init
t_bme = bme280_read_temp()
p_bme = bme280_read_pressure()
p_bme = Psl(p_bme,alt)
h_bme = bme280_read_humidity()
PRINT "T= ";t_bme;" P= ";p_bme;" H= ";h_bme
I2C CLOSE

END

FUNCTION Psl(p AS FLOAT, alt AS FLOAT) AS FLOAT
'given local pressure and altitude, returns pressure at sea level
Psl= p/(1- alt/44330.77)^5.25588
END FUNCTION

'
FUNCTION bme280_read_temp() AS FLOAT
LOCAL INTEGER var1,var2,adc_T
LOCAL adc%(2),n!
I2C WRITE BME280_ADDRESS,1,1,BME280_REGISTER_TEMPDATA
I2C READ BME280_ADDRESS,0,3,adc%()
adc_T=((adc%(0)<<16) OR (adc%(1)<<8) OR adc%(2))>>4
var1 = ((((adc_T>>3) - (T1 <<1))) * T2) \ q(11)
var2 = (((((adc_T>>4) - (T1)) * ((adc_T\ q(4)) - (T1))) \ q(12)) * (T3)) \ q(14)
t_fine = var1 + var2
bme280_read_temp = ((t_fine * 5 + 128) \ q(8))/100.0
PRINT "bme280_read_temp()"
FOR n! = 0 TO 2
PRINT "adc%(";n!;"), ";adc%(n!)
NEXT n!
END FUNCTION

FUNCTION bme280_read_pressure() AS FLOAT
LOCAL INTEGER var1, var2, adc_P, p
LOCAL adc%(2),n!
I2C WRITE BME280_ADDRESS,1,1,BME280_REGISTER_PRESSUREDATA
I2C READ BME280_ADDRESS,0,3,adc%()
adc_P=((adc%(0)<<16) OR (adc%(1)<<8) OR adc%(2))>>4
var1 = t_fine - 128000
var2 = var1 * var1 * P6
var2 = var2 + ((var1 * P5)<<17)
var2 = var2 + (P4 << 35)
var1 = ((var1 * var1 * P3)\ q(8)) + ((var1 * P2)<<12)
var1 = ((1<<47)+var1)*P1\ q(33)
IF var1 = 0 THEN
bme280_read_pressure = 0' avoid exception caused by division by zero
EXIT FUNCTION
ENDIF
p = 1048576 - adc_P
p = (((p<<31) - var2)*3125) \ var1
var1 = (P9 * (p\ q(13)) * (p\ q(13))) \ q(25)
var2 = (P8 * p) \ q(19)
p = ((p + var1 + var2) \ q(8)) + (P7<<4)
bme280_read_pressure = p/25600.0
PRINT "bme280_read_pressure()"
FOR n! = 0 TO 2
PRINT "adc%(";n!;"), ";adc%(n!)
NEXT n!
END FUNCTION
'
FUNCTION bme280_read_humidity() AS FLOAT
LOCAL INTEGER v_x1,adc_H
LOCAL adc%(1),n!
I2C WRITE BME280_ADDRESS,1,1,BME280_REGISTER_HUMIDDATA
I2C READ BME280_ADDRESS,0,2,adc%()
adc_H=(adc%(0)<<8) OR adc%(1)
v_x1 = t_fine - 76800
v_x1=(((((adc_H<<14)-((H4)<<20)-(H5*v_x1))+16384)\ q(15))*(((((((v_x1*H6)\ q(10))*(((v_x1*H3)\ q(11))+32768))\ q(10))+2097152)*H2+8192)\ q(14)))
v_x1 = (v_x1 - (((((v_x1 \ q(15)) * (v_x1 \ q(15))) \ q(7)) * (H1)) \ q(4)))
IF v_x1< 0 THEN v_x1 = 0
IF v_x1 > 419430400 THEN v_x1= 419430400
bme280_read_humidity = (v_x1\ q(12)) / 1024.0
PRINT "bme280_read_pressure()"
FOR n! = 0 TO 1
PRINT "adc%(";n!;"), ";adc%(n!)
NEXT n!
END FUNCTION

SUB bme280_init
LOCAL i%,cal%(17),n!
' i2c open 400,1000 '400KHz bus speed
I2C WRITE BME280_ADDRESS,1,1,BME280_REGISTER_CHIPID
I2C READ BME280_ADDRESS,0,1,i%
IF i%<>&H60 THEN PRINT "Error BME280 not found"
'
I2C WRITE BME280_ADDRESS,1,1,BME280_REGISTER_T1
I2C READ BME280_ADDRESS,0,6,cal%()
T1=cal%(0) OR (cal%(1)<< 8)
T2=cal%(2) OR (cal%(3)<< 8): IF T2 AND s16b THEN T2=T2 OR s16 'sign extend if required
T3=cal%(4) OR (cal%(5)<< 8): IF T3 AND s16b THEN T3=T3 OR s16
'
I2C WRITE BME280_ADDRESS,1,1,BME280_REGISTER_P1
I2C READ BME280_ADDRESS,0,18,cal%()
P1=cal%(0) OR (cal%(1)<<8)
P2=cal%(2) OR (cal%(3)<<8): IF P2 AND s16b THEN P2=P2 OR s16 'sign extend if required
P3=cal%(4) OR (cal%(5)<<8): IF P3 AND s16b THEN P3=P3 OR s16
P4=cal%(6) OR (cal%(7)<<8): IF P4 AND s16b THEN P4=P4 OR s16
P5=cal%(8) OR (cal%(9)<<8): IF P5 AND s16b THEN P5=P5 OR s16
P6=cal%(10) OR (cal%(11)<<8): IF P6 AND s16b THEN P6=P6 OR s16
P7=cal%(12) OR (cal%(13)<<8): IF P7 AND s16b THEN P7=P7 OR s16
P8=cal%(14) OR (cal%(15)<<8): IF P8 AND s16b THEN P8=P8 OR s16
P9=cal%(16) OR (cal%(17)<<8): IF P9 AND s16b THEN P9=P9 OR s16
'
I2C WRITE BME280_ADDRESS,1,1,BME280_REGISTER_H1
I2C READ BME280_ADDRESS,0,1,H1
I2C WRITE BME280_ADDRESS,1,1,BME280_REGISTER_H2
I2C READ BME280_ADDRESS,0,7,cal%()
H2=cal%(0) OR (cal%(1)<< 8): IF H2 AND s16b THEN H2=H2 OR s16 'sign extend if required
H3=cal%(2)
H6=cal%(6): IF H6 AND s8b THEN H6=H6 OR s8 'sign extend if required
H4=(cal%(3)<<4) OR (cal%(4) AND &H0F): IF H4 AND s12b THEN H4=H4 OR s12 'sign extend if required
H5=(cal%(5)<<4) OR (cal%(4)>>4): IF H5 AND s12b THEN H5=H5 OR s12
'
I2C WRITE BME280_ADDRESS,0,2,BME280_REGISTER_CONTROLHUMID,&H05 '16x oversampling humidity
I2C WRITE BME280_ADDRESS,0,2,BME280_REGISTER_CONTROL,&HB7 '16x oversampling pressure/temp, normal mode
'
FOR n! = 0 TO 17
PRINT "cal%(";n!;"), &h";HEX$(cal%(n!),2)
NEXT n!
PRINT
PRINT "T1 , &h";HEX$(T1,4)
PRINT "T2 , &h";HEX$(T2,4)
PRINT "T3 , &h";HEX$(T3,4)
PRINT
PRINT "P1 , &h";HEX$(P1,4)
PRINT "P2 , &h";HEX$(P2,4)
PRINT "P3 , &h";HEX$(P3,4)
PRINT "P4 , &h";HEX$(P4,4)
PRINT "P5 , &h";HEX$(P5,4)
PRINT "P6 , &h";HEX$(P6,4)
PRINT "P7 , &h";HEX$(P7,4)
PRINT "P8 , &h";HEX$(P8,4)
PRINT "P9 , &h";HEX$(P9,4)
PRINT
PRINT "H1 , &h";HEX$(H1,4)
PRINT "H2 , &h";HEX$(H2,4)
PRINT "H3 , &h";HEX$(H3,4)
PRINT "H4 , &h";HEX$(H4,4)
PRINT "H5 , &h";HEX$(H5,4)
PRINT "H6 , &h";HEX$(H6,4)
PRINT
END SUB
'
FUNCTION q(x AS INTEGER) AS INTEGER 'returns 2 raised to the power
q=(1<<x)
END FUNCTION

Results form a RPi and micromite:

Quote > RUN
Device = Micromite MkII
cal%( 0), &h6D
cal%( 1), &h01
cal%( 2), &h00
cal%( 3), &h13
cal%( 4), &h27
cal%( 5), &h03
cal%( 6), &h1E
cal%( 7), &h26
cal%( 8), &h37
cal%( 9), &hFF
cal%( 10), &hF9
cal%( 11), &hFF
cal%( 12), &hAC
cal%( 13), &h26
cal%( 14), &h0A
cal%( 15), &hD8
cal%( 16), &hBD
cal%( 17), &h10

T1 , &h6D04
T2 , &h663A
T3 , &h0032

P1 , &h9613
P2 , &hFFFFFFFFFFFFD5D0
P3 , &h0BD0
P4 , &h26AE
P5 , &hFFFFFFFFFFFFFF37
P6 , &hFFFFFFFFFFFFFFF9
P7 , &h26AC
P8 , &hFFFFFFFFFFFFD80A
P9 , &h10BD

H1 , &h004B
H2 , &h016D
H3 , &h0000
H4 , &h0137
H5 , &h0032
H6 , &h001E

bme280_read_temp()
adc%( 0), 125
adc%( 1), 97
adc%( 2), 160
bme280_read_pressure()
adc%( 0), 66
adc%( 1), 52
adc%( 2), 240
bme280_read_pressure()
adc%( 0), 108
adc%( 1), 72
T= 20.91 P= 1027.35 H= 43.3281
>

> RUN
Device = Pi-cromite running on H/W version: A02082
cal%( 0), &h6D
cal%( 1), &h01
cal%( 2), &h00
cal%( 3), &h13
cal%( 4), &h27
cal%( 5), &h03
cal%( 6), &h1E
cal%( 7), &h26
cal%( 8), &h37
cal%( 9), &hFF
cal%( 10), &hF9
cal%( 11), &hFF
cal%( 12), &hAC
cal%( 13), &h26
cal%( 14), &h0A
cal%( 15), &hD8
cal%( 16), &hBD
cal%( 17), &h10

T1 , &h6D04
T2 , &h663A
T3 , &h0032

P1 , &h9613
P2 , &hFFFFFFFFFFFFD5D0
P3 , &h0BD0
P4 , &h26AE
P5 , &hFFFFFFFFFFFFFF37
P6 , &hFFFFFFFFFFFFFFF9
P7 , &h26AC
P8 , &hFFFFFFFFFFFFD80A
P9 , &h10BD

H1 , &h004B
H2 , &h016D
H3 , &h0000
H4 , &h0137
H5 , &h0032
H6 , &h001E

bme280_read_temp()
adc%( 0), 126
adc%( 1), 87
adc%( 2), 112
bme280_read_pressure()
adc%( 0), 66
adc%( 1), 134
adc%( 2), 128
bme280_read_pressure()
adc%( 0), 107
adc%( 1), 206
T= 22.14 P= 1027.339211 H= 42.65429687
>

Jim

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MMedit MMBasic Help

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